This invention relates to processing oil shale, and more particularly, to an oil shale retorting process for producing explosives.
Researchers have now renewed their efforts to find alternate sources of energy and hydrocarbons in view of recent rapid increases in the price of crude oil and natural gas. Much research has been focused on recovering hydrocarbons from solid hydrocarbon-containing material such as oil shale, coal and tar sands by pyrolysis or upon gasification to convert the solid hydrocarbon-containing material into more readily usable gaseous and liquid hydrocarbons.
Vast natural deposits of oil shale found in the United States and elsewhere contain appreciable quantities of organic matter known as "kerogen" which decomposes upon pyrolysis or distillation to yield oil, gases and residual carbon. It has been estimated that an equivalent of 7 trillion barrels of oil are contained in oil shale deposits in the United States with almost sixty percent located in the rich Green River oil shale deposits of Colorado, Utah and Wyoming. The remainder is contained in the leaner Devonian-Mississippian black shale deposits which underlie most of the eastern part of the United States.
As a result of dwindling supplies of petroleum and natural gas, extensive efforts have been directed to develop retorting processes which will economically produce shale oil on a commercial basis from these vast resources.
Generally, oil shale is a fine-grained sedimentary rock stratified in horizontal layers with a variable richness of kerogen content. Kerogen has limited solubility in ordinary solvents and therefore cannot be readily recovered by extraction. Upon heating oil shale to a sufficient temperature, the kerogen is thermally decomposed to liberate vapors, mist, and liquid droplets of shale oil and light hydrocarbon gases such as methane, ethane, ethene, propane and propene, as well as other products such as hydrogen, nitrogen, carbon dioxide, carbon monoxide, ammonia, steam and hydrogen sulfide. A carbon residue typically remains on the retorted shale.
Shale oil is not a naturally occurring product, but is formed by the pyrolysis of kerogen in the oil shale. Crude shale oil, sometimes referred to as "retort oil," is the liquid oil product recovered from the liberated effluent of an oil shale retort. Synthetic crude oil (syncrude) is the upgraded oil product resulting from the hydrogenation of crude shale oil.
The process of pyrolyzing the kerogen in oil shale, known as retorting, to form liberated hydrocarbons, can be done in surface retorts in aboveground vessels or in in situ retorts under ground. In principle, the retorting of shale and other hydrocarbon-containing materials, such as coal and tar sands, comprises heating the solid hydrocarbon-containing material to an elevated temperature and recovering the vapors and liberated effluent. However, as medium grade oil shale yields approximately 20 to 25 gallons of oil per ton of shale, the expense of materials handling is critical to the economic feasibility of a commercial operation.
In situ retorts require less mining and handling than surface retorts. In vertical in situ retorts, a flame front moves downward through a rubblized bed of oil shale to liberate shale oil, off gases and condensed water. There are two types of in situ retorts: true in situ retorts and modified in situ retorts. In true in situ retorts, none of the shale is mined, holes are drilled into the formation and the oil shale is explosively rubblized, if necessary, and then retorted. In modified in situ retorts, some of the oil shale is removed by mining before being explosively rubblized to create a cavity which provides extra space for explosively expanded oil shale. The oil shale which has been removed is conveyed to the surface and retorted above ground.
Typifying the many methods of in situ retorting and explosively forming in situ retorts are those found in U.S. Pat. Nos. 1,913,395; 1,191,636; 2,418,051; 3,001,776; 3,586,377; 3,434,757; 3,661,423; 3,951,456; 3,980,339; 4,007,963; 4,017,119; 4,105,251; 4,120,355; 4,126,180; 4,133,380; 4,149,752; 4,153,300; 4,158,467; 4,177,886; 4,185,871; 4,194,788; 4,199,026; 4,210,867; 4,210,868; 4,231,617; 4,243,100; 4,263,969; 4,265,486; 4,266,608; 4,271,904; 4,315,656; 4,323,120; 4,323,121; 4,328,863; 4,343,360; 4,343,361; 4,353,418; and 4,378,949.
In surface retorting, oil shale is mined from the ground, brought to the surface, crushed and placed in vessels where it is contacted with a hot solid heat carrier material, such as hot spent shale, ceramic balls, metal balls, or sand or a gaseous heat carrier material, such as light hydrocarbon gases, for heat transfer. The resulting high temperatures cause shale oil to be liberated from the oil shale leaving a retorted, inorganic material and carbonaceous material such as coke. The carbonaceous material can be burned by contact with oxygen at oxidation temperatures to recover heat and to form a spent oil shale relatively free of carbon. Spent oil shale which has been depleted in carbonaceous material is removed from the retort and recycled as heat carrier material or discarded. The combustion gases are dedusted in cyclones or electrostatic precipitators.
Surface retorting with solid heat carrier material has many advantages. The solid heat carrier material should be well mixed with the raw shale to enhance heat exchange and conversion of kerogen to shale oil and light hydrocarbon gases. There are many types of surface retorting processes. In the Lurgi-Ruhrgas process, spent shale is mechanically mixed with raw oil shale in a screw conveyor. In the Tosco II process, ceramic or metal balls (solid heat carrier material) are mechanically mixed with raw oil shale in a rotating pyrolysis drum. In the Union process, raw oil shale is retorted in a rock pump retort with a gaseous heat carrier medium. In the Parahoe process, raw oil shale is retorted in a moving grate retort. In fluid bed processes, spent shale is fluidly (turbulently) mixed with raw oil shale in the presence of a pressurized fluidizing gas. In static mixer and gravity flow processes, spent shale is mixed with raw oil shale in uninterrupted free fall or by gravity flow with the aid of stationary internals in a static mixer or gravity flow retort.
During fluid bed, moving bed and other types of surface retorting, decrepitation of oil shale occurs when particles of oil shale collide with each other and impinge against the walls of the retort forming minute entrained particulates of shale dust. The use of hot spent shale as heat carrier material can aggravate the dust problem. Shale dust is also emitted and carried away with the effluent product stream during modified in situ retorting as a flame front passes through a fixed bed of rubblized shale, as well as in fixed bed surface retorting, but dust emission is not as severe as in other types of surface retorting.
Shale dust ranges in size from less than 1 micron to 1000 microns and is entrained and carried away with the effluent product stream. Because shale dust is so small, it cannot be effectively removed to commercially acceptable levels by conventional dedusting equipment.
The rotorting, carbonization or gasification of coal, peat and lignite and the retorting or extraction of tar sands and gilsonite may create similar dust problems.
After retorting, the effluent product stream of liberated hydrocarbons and entrained dust is withdrawn from the retort through overhead lines and subsequently conveyed to a separator, such as a single or multiple stage distillation column, quench tower, scrubbing cooler or condenser, where it is separated into fractions of light gases, light oils, middle oils and heavy oils with the bottom heavy oil fraction containing essentially all of the dust. As much as 65% by weight of the bottom heavy oil fraction consists of dust.
It is very desirable to upgrade the bottom heavy oil into more marketable products, such as light oils and middle oils, but the heavy oil fraction is laden with dust and it is very viscous and cannot be pipelined. Dust laden heavy oil plugs up hydrotreaters and catalytic crackers, gums up valves, heat exchangers, outlet orifices, pumps and distillation towers, builds up insulative layers on heat exchange surfaces reducing their efficiency and fouls up other equipment. Furthermore, the dusty heavy oil corrodes turbine blades and creates emission problems. Moreover, the dusty heavy oil cannot be refined with conventional equipment.
In an effort to solve this dust problem, gas-solid separation devices, such as electrostatic precipitators have been used as well as cyclones located both inside and outside the retort. Electrostatic precipitators and cyclones, however, must be operated at high temperatures and the product stream must be maintained at or above the temperature attained during the retorting process to prevent any condensation and accumulation of dust on processing equipment. Maintaining the effluent steam at high temperatures is not only expensive from an energy standpoint, but it allows detrimental side reactions, such as cracking, coking and polymerization of the effluent product stream, which tends to decrease the yield and quality of condensable hydrocarbons.
Over the years various processes and equipment have been suggested to decrease the dust concentration in the heavy oil fraction and/or upgrade the heavy oil into more marketable light oils and medium oils. Such prior art dedusting processes and equipment have included the use of cyclones, electrostatic precipitators, pebble beds, scrubbers, filters, spiral tubes, ebullated bed catalytic hydrotreaters, desalters, autoclave settling zones, sedimentation, gravity settling, percolation, hydrocloning, magnetic separation, electrical precipitation, stripping and binding, as well as the use of diluents, solvents and chemical additives before centrifuging. Typifying those prior art processes and equipment and related processes and equipment are those found in U.S. Pat. Nos. 2,235,639; 2,717,865; 2,719,114; 2,723,951; 2,793,104; 2,879,224; 2,899,736; 2,904,499; 2,911,349; 2,952,620; 2,968,603; 2,982,701; 3,008,894; 3,034,979; 3,058,903; 3,252,886; 3,255,104; 3,468,789; 3,560,369; 3,684,699; 3,703,442; 3,784,462; 3,799,855; 3,808,120; 3,900,389; 3,901,791; 3,929,625; 3,974,073; 3,990,885; 4,028,222; 4,040,958; 4,049,540; 4,057,490; 4,069,133; 4,080,285; 4,088,567; 4,105,536; 4,151,073; 4,159,949; 4,162,965; 4,166,441; 4,182,672; 4,199,432; 4,220,522; and 4,246,093 as well as in the articles by Rammler, R. W., The Retorting of Coal, Oil Shale and Tar Sand By Means of Circulated Fine-Grained Heat Carriers as a Preliminary Stage in the Production of Synthetic Crude Oil, Volume 65, Number 4, Quarterly of the Colorado School of Mines, pages 141-167 (October 1970) and Schmalfeld, I. P., The Use of The Lurgi/Ruhrgas Process For The Distillation of Oil Shale, Volume 70, Number 3, Quarterly of the Colorado School of Mines, pages 129-145 (July 1975). These prior art processes and equipment have not been successful in decreasing the dust concentration in the heavy oil fraction to commercially acceptable levels.
Over the years many different types of explosives, blasting agents and incendiary devices have been developed. Some of the more widely used explosives that have been around for decades, are nitroglycerin (dynamite) and trinitrotoluene (TNT). In recent years ammonium nitrate fuel oil (ANFO) has been the most widely used explosive because it is less expensive and more effective than dynamite and TNT. ANFO is a mixture of ammonium nitrate and No. 2 diesel fuel oil. Typifying the many types of explosives, blasting agents and incendiary devices are those shown in U.S. Pat. Nos. 2,530,491; 2,615,800; 2,886,424; 2,975,046; 2,987,389; 3,004,842; 3,032,450; 3,094,069; 3,147,163; 3,150,019; 3,180,768; 3,240,641; 3,279,965; 3,388,014; 3,447,978; 3,453,155; and 3,722,410, as well as in the SME Mining Engineering Handbook, published by the Society of Mining Engineers of the American Institute of Mining, Metallurgical, and Petroleum Engineers Inc., pages 11-88 to 11-96 and pages 17-139 to 17-142, Volume 1 (1973) and in the article by Clark, G. B., Basic Properties of Ammonium Nitrate Fuel Oil Explosives (ANFO), Volume 76, Number 1, Quarterly of the Colorado School of Mines, pages 1-32 (January, 1981). These explosives, blasting agents and incendiary devices have met with varying degrees of success.
It is therefore desirable to provide an improved oil shale retorting process and explosive which overcomes most, if not all, of the preceding problems.